At 5am beneath the Shivalik hills in northern India, Swami Ramdev sits cross-legged swaddled in saffron robes commanding the rapt attention of 500 devotees of his brand of yoga. The crowd is made up mostly of middle-class Indians, many suffering from chronic conditions for which traditional medicine has little to offer but comfort.

Each "patient" has paid 7,000 to 40,000 rupees (£90 to £500) to be among the first to spend a week at the swami's newest venture: a village of 300 bungalows offering spiritual retreat in the shadow of eucalyptus trees.

Swami Ramdev's pitch is that pranayama, the ancient Indian art of breath control, can cure a bewildering array of diseases. "Asthma, arthritis, sickle-cell anaemia, kidney problems, thyroid disease, hepatitis, slipped discs - and it will unblock any fallopian tubes," he tells his audience in the yoga village, who line up to have their blood tested and receive herbal remedies.

Although India has a long tradition of mystical gurus, Swami Ramdev represents a new phenomenon: the television yoga evangelist. Almost all his congregation have been drawn through his shows on India's Aastha channel.

Every morning, the swami appears on television chanting prayers and explaining that ailments, physical and mental, can be treated by what looks like little more than sharp intakes of air and painful-looking body contortions. More than 20 million tune in each day in India alone. The television guru, who is also known as Baba Ramdev, is also available across the world - including Britain.

He has just finished teaching on a yoga cruise from India to China, which even after attracting corporate sponsorship still charged disciples £1,000 a ticket. Last year he appeared in Westminster to give British politicians a chance to sample his yogic wisdom.

Ludy Mantri, a housewife from Mauritius, has paid 40,000 rupees and travelled 4,000 miles to see "her swami" in the Haridwar yoga village in the hope he can help her find a cure for diabetes.

"I have been on medicines every day for the last 12 years. The chanting of Om has an amazing effect and the words of Ramdev energise one through the day."

Born into a farming family in north India he retains a common touch, making rustic jokes in chaste Hindi. The guru combines this with a gentle manner and a knack for public relations. The swami sells himself as a one-person health service. He says he only charges the wealthy and that the poor get his medicines for free. He has 500 hospitals in India serving more than 30,000 a day.

It is no surprise that many sections of the Indian elite - including judges, ministers and Bollywood stars - have visited his camps. Such is his popularity that the Indian army incorporated Ramdev's techniques claiming it made for a "deadlier fighting force".

Ramdev often speaks less of spiritualism and more of the need to develop his country through yoga, portraying himself as an Indian nationalist. He attacks multinational companies for seeking to drain India of profits. He calls Coke and Pepsi good only for "toilet cleaning".

In a country where renunciation is seen as almost a divine virtue, Ramdev announces that he has long ago given up sex - because "it is not love".

The adoration he inspires was seen in 2006 when Indian communists accused the guru of using human bones and animal parts in ayurvedic drugs produced by his pharmacy. His followers rioted and attacked the party headquarters. The Communist party backed down when it saw where public sympathy lay.

In an interview with the Guardian, Ramdev said that the problem with communists was that they did not have "faith in spirituality and are philosophically against religion. My cures are clean but the communists have an agenda."

There is little controversy about his basic assertions. He says that following his yoga teachings for 30 minutes a day, along with a vegetarian diet of raw or lightly boiled food and no alcohol or tobacco, clears clogged arteries, reduces blood sugar and lowers blood pressure.

But the swami defended his more extravagant claims that yoga could cure terminal illnesses such as cancer. He also said he had evidence that breathing exercises could help Aids patients recover by enabling a rise in the number of cells that the HIV virus destroys.

Ramdev has an explanation for his success with cancer - that yoga oxygenates the blood which kills the tumour. "Yoga is self-healing and self-realisation. I have many cases of cancer which I can provide where patients have recovered. We have cured blood, throat, ovarian, uterine and throat cancers with yoga."

In the case of HIV, he says scientists "have not understood [it] properly". He says that "through yoga and lifestyle changes people increase their CD4 count [the cells the HIV virus attacks]. The truth seen for the first time does appear like a miracle."

Such claims have angered many doctors. Mohammed Abbas, The president of the Indian Medical Association, said that although yoga is "good exercise, it cannot be used to make ridiculous claims about curing HIV or cancer. This is false hope for ill people."

The swami says patients are tested and improvements measured by "independent" doctors. Asked whether he has run any tests to analyse treatment, he offers a book of testimonies from disciples convinced they have been cured of cancer, cirrhosis and kidney failure.

Some have called for the swami to be prosecuted for "peddling quackery of the highest order".

"Claiming such absurdities is against the law," said Sanal Edamaruku of the Indian Rationalist Association. "The magical remedies act of 1954 was brought in to stop people such as Baba Ramdev from promoting dangerous ideas about curing cancer and the like.

"The political class is running scared of this man and the backlash that such a prosecution might unleash."